Principles of Metabolism

Question 1

What are the inputs and outputs of carbohydrate catabolism?

Answer 1

Inputs:
- glucose = fuel
- O2 = oxidizing agent
- ADP + Pi = dead battery

Outputs
- CO2 = spent fuel
- H2O = reduced O2
- ATP = recharged battery

Question 2

How many net ATPs is produced per molecule of glucose (including cell respiration)?

Answer 2

32 ATPs

Question 3

Do molecules with more or less reduced carbons yield more energy upon oxidation?

Answer 3

more because the more reduced a carbon is, the more electrons it “owns” and thus more energy can be extracted from that carbon because there are more electrons we can pull from that molecule

Question 4

What do NADH and FADH2 do in catabolism?

Answer 4

• they store electrons extracted during catabolism
• oxidized form: NAD+
• reduced form: NADH

Question 5

Is NAD+ or NADP used in catabolism?

Answer 5

• NAD+ is in catabolism
• NADP is in anabolism

Question 6

Where is the energy stored in ATP?

Answer 6

• stored in the phosphoanhydride bonds of ATP

Question 7

Why is biologically active ATP bound to Mg2+?

Answer 7

The negative charges in the phosphate groups don’t like being close together, so in the cell, ATP is usually found in complex with Mg2+ because it needs a large positive charge to balance it

Question 8

What groups in hydrolysis have high “transfer potential”?

Answer 8

• the beta and gamma phosphoryl groups

Question 9

Why is ATP hydrolysis highly exergonic (favorable)?

Answer 9

• the electrostatic impulsion is relieved
• the Pi is stabilized by resonance
• the products of the reaction readily ionize
• and Q/K &laquo_space;1

Question 10

Why does ATP not degrade immediately?

Answer 10

• doesn’t degrade immediately despite ATP hydrolysis because there’s a transition state, so there is some energy barrier

Question 11

What’s the logic of coupled reactions?

Answer 11

• use the energy from one reaction to carry out the other

Question 12

What’s an example of a coupled reaction?

Answer 12

• glucokinase

Question 13

What does phosphocreatine do?

Answer 13

• regenerates ATP in skeletal muscle during exercise

Question 14

In the mitochondria, what are the relative concentrations of ATP and PCr (phosphocreatine)?

Answer 14

• [ATP] = high
• [PCR] = low
• since [PCR] is low, that drives the energy creation of more PCR

Question 15

What are the relative concentrations of ATP and PCr in the cytosol during exercise?

Answer 15

• [PCr] = high
• [ADP] high-ish
• ATP regeneration because [PCr] is high, the equilibrium is pushed towards ATP regeneration

Question 16

Explain how the active site of creatine kinase works?

Answer 16

• ADP - Mg2+ and creatine are bound in close proximity
• 5 arginines will coordinate those negative charges and phosphate will form a trigonal transition state in between creatine and ADP, and it can go in either direction
• hydrophobic residues nearby contribute to specificity by packing against the creatine methyl

Question 17

How is metabolic flux regulated?

Answer 17

• regulated by kinetic control
• regulation of enzymes